The demand for newer battery materials having higher energy density, lower toxicity, and lower material cost has led researchers and battery manufacturers to consider lithium-sulfur based systems. The lithium-sulfur chemistry offers a theoretical energy density almost ten times that achieved by current battery systems. Unfortunately, lithium-sulfur batteries have traditionally suffered from low sulfur utilization resulting in a low capacity and severe capacity fade, thereby providing a short lifetime.
Three main approaches to limit capacity loss upon cycling sulfur-based cathodes have been developed. One approach to circumvent capacity fade has been to tether sulfur within a cathode material with an organic molecular chain. This approach attempts to prevent the sulfur from migrating out of the cathode material and becoming electrochemically useless by using the organic molecular chain to attach to the sulfur and/or sulfur-containing species. Such an approach has been investigated and disclosed in U.S. Pat. Nos. 4,833,048; 5,162,175; 5,516,598; 5,529,860; 5,601,947; 6,117,590; and 6,309,778. A second approach to limit the capacity fade of a lithium battery due to sulfur migration from the cathode has been to use an additive to bind polysulfides created within the battery system. This approach has been disclosed in U.S. Pat. Nos. 5,532,077; 6,210,831; and 6,406,814. Materials used for this approach include carbon, silica, metal oxides, transition metal chalcogenides and metals. The third approach has been to use mixed metal chalcogenides containing sulfur as the electrochemically active material within the cathode as disclosed in U.S. Pat. Nos. 6,300,009; 6,319,633; and 6,376,127. However, despite numerous attempts to improve the performance of lithium batteries containing sulfur within the cathode, a significant improvement in cycle life without severely limiting capacity has remained elusive. As such, a sulfur cathode having a relatively high capacity with improved cycle life would be desirable.